1. Field of the Invention
The present invention relates to a fuel cell generator using a solid-electrolyte having an ion conductivity.
2. Related Art Statement
Recently, a fuel cell has been studied as an electric generator. This fuel cell generator can convert an chemical energy directly into an electric energy, and thus there is no limitation of Carnot cycle. Therefore, a high energy converting efficiency can be realized, and various fuels such as naphtha, natural as, methanol, coal improved gas, heavy oil, etc. can be utilized. Further, generation of public nuisance is low, and power generating efficiency is not varied corresponding to a size of the apparatus.
Since a fuel cell utilizing a solid-electrolyte i.e. solid oxide fuel cell (hereinafter, abbreviated as SOFC) can be used at high temperatures such as 1000.degree. C., an electrode reaction is extremely active, and it is not necessary to use an expensive precious metal such as platinum. Moreover, in the SOFC, since polarization is low and a generated output voltage is relatively high, an energy converting efficiency become extremely higher as compared with the other fuel cell. Further, since all the members constructing the SOFC are solid members, a safety SOFC having a long life can be obtained.
An SOFC element comprises generally air electrodes, solid-electrolyte members, and fuel electrodes. A plate-like SOFC element has a large effective area fraction per unit volume as a cell, and thus it is desirable for the SOFC. There is known a fuel cell generator comprising a plurality of plate-like SOFC elements arranged parallelly and power generating rooms formed rigidly in a sealed manner between the SOFC elements, wherein oxygen gas and fuel gas are supplied from one end side of respective power generating rooms and burnt exhaust gas is discharged from the other end side of the power generating rooms.
However, in the fuel cell generator mentioned above wherein respective unit SOFC elements are sealed rigidly with each other, since respective unit SOFC elements are restricted with each other to form an airtight power generating room, stresses are generated at edge portions of the unit SOFC element, and thermal stresses due to high temperatures during the operation are enlarged by this restriction. Moreover, an electrode reaction is active in the vicinity of a fuel gas supply inlet and thus a temperature is high, but it is inactive in the vicinity of a fuel gas discharge outlet and thus a temperature is low. Therefore, a large temperature gradient is generated in the power generating room, and thus large thermal stresses are generated. These stresses generate cracks in the fragile SOFC element, and as a result, a power generating efficiency is lowered and a cell collector starts to be broken.